Mitochondria can show tremendous variation in size, even within a single cell. Here, a huge spherical mitochondria of about 6-7 µm in diameter is adjacent to small elongate mitochondria 0.5 µm wide in a testicular Leydig cell of the ground squirrel Citellus lateralis. This image is courtesy of Jeffrey Pudney, and appears as Figure 247 in Chapter 7 (Mitochondria) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the accompanying chapter is available on the ASCB’s BioEDUCATE website.